131I Ablation of an Entire Thyroid Gland in Locally Invasive Differentiated Thyroid Cancer Without Surgery.

ABSTRACT: A 79-year-old man with locally metastatic papillary thyroid cancer to left-sided cervical lymph nodes was referred for radioiodine therapy. He was considered unfit for thyroidectomy due to extensive local involvement and severe interstitial lung disease requiring continuous oxygen. The patient was treated with low doses of radioiodine (approximately 30 mCi) every 6 months with corticosteroid cover for 3 years with good effect. Sequential 131I scanning and serum thyroglobulin levels confirmed virtual complete ablation of the thyroid gland. The patient remained well on thyroid hormone replacement.

Comparison of radiobiological parameters for 90Y radionuclide therapy (RNT) and external beam radiotherapy (EBRT) in vitro.

BACKGROUND: Dose rate variation is a critical factor affecting radionuclide therapy (RNT) efficacy. Relatively few studies to date have investigated the dose rate effect in RNT. Therefore, the aim of this study was to benchmark 90Y RNT (at different dose rates) against external beam radiotherapy (EBRT) in vitro and compare cell kill responses between the two irradiation processes. RESULTS: Three human colorectal carcinoma (CRC) cell lines (HT29, HCT116, SW48) were exposed to 90Y doses in the ranges 1-10.4 and 6.2-62.3 Gy with initial dose rates of 0.013-0.13 Gy/hr (low dose rate, LDR) and 0.077-0.77 Gy/hr (high dose rate, HDR), respectively. Results were compared to a 6-MV photon beam doses in the range from 1-9 Gy with constant dose rate of 277 Gy/hr. The cell survival parameters from the linear quadratic (LQ) model were determined. Additionally, Monte Carlo simulations were performed to calculate the average dose, dose rate and the number of hits in the cell nucleus. For the HT29 cell line, which was the most radioresistant, the α/ß ratio was found to be ≈ 31 for HDR-90Y and ≈ 3.5 for EBRT. LDR-90Y resulting in insignificant cell death compared to HDR-90Y and EBRT. Simulation results also showed for LDR-90Y, for doses ≲ 3 Gy, the average number of hits per cell nucleus is ≲ 2 indicating insufficiently delivered lethal dose. For 90Y doses [Formula: see text] 3 Gy the number of hits per nucleus decreases rapidly and falls below ≈ 2 after ≈ 5 days of incubation time. Therefore, our results demonstrate that LDR-90Y is radiobiologically less effective than EBRT. However, HDR-90Y at ≈ 56 Gy was found to be radiobiologically as effective as acute ≈ 8 Gy EBRT. CONCLUSION: These results demonstrate that the efficacy of RNT is dependent on the initial dose rate at which radiation is delivered. Therefore, for a relatively long half-life radionuclide such as 90Y, a higher initial activity is required to achieve an outcome as effective as EBRT.

Accuracy of Dose Calibrators for 68Ga PET Imaging: Unexpected Findings in a Multicenter Clinical Pretrial Assessment.

We report the discovery of a systematic miscalibration during the work-up process for site validation of a multicenter clinical PET imaging trial using 68Ga, which manifested as a consistent and reproducible underestimation in the quantitative accuracy (assessed by SUV) of a range of PET systems from different manufacturers at several different facilities around Australia. Methods: Sites were asked to follow a strict preparation protocol to create a radioactive phantom with 68Ga to be imaged using a standard clinical protocol before commencing imaging in the trial. All sites had routinely used 68Ga for clinical PET imaging for many years. The reconstructed image data were transferred to an imaging core laboratory for analysis, along with information about ancillary equipment such as the radionuclide dose calibrator. Fourteen PET systems were assessed from 10 nuclear medicine facilities in Australia, with the aim for each PET system being to produce images within 5% of the true SUV. Results: At initial testing, 10 of the 14 PET systems underestimated the SUV by 15% on average (range, 13%-23%). Multiple PET systems at one site, from two different manufacturers, were all similarly affected, suggesting a common cause. We eventually identified an incorrect factory-shipped dose calibrator setting from a single manufacturer as being the cause. The calibrator setting for 68Ga was subsequently adjusted by the users so that the reconstructed images produced accurate values. Conclusion: PET imaging involves a chain of measurements and calibrations to produce accurate quantitative performance. Testing of the entire chain is simple, however, and should form part of any quality assurance program or prequalifying site assessment before commencing a quantitative imaging trial or clinical imaging.

68Ga-DOTATATE Breast Uptake and Expression in Breast Milk.

The excretion of Ga-DOTA-Octreotate (DOTATATE) and related somatostatin analogues in breast milk has not been demonstrated. We report a case of a 34-year-old woman, 7 months postpartum and breastfeeding, who was referred for DOTATATE imaging after the diagnosis of appendiceal carcinoid and subsequent appendectomy. Prominent breast uptake was noted. A breast milk sample from the patient at 90 minutes postinjection was assayed in a gamma counter and shown to have a concentration of 5.6 Bq/g per MBq administered. The excretion of DOTATATE in breast milk is important to consider when providing radiation safety advice to breastfeeding patients.

Quantitative (90)Y image reconstruction in PET.

PURPOSE: Positron emission tomography (PET) imaging is increasingly used to confirm localization of (90)Y microspheres in the treatment of liver cancer. The aim of this work was to evaluate the quantification of (90)Y PET data on a current generation time-of-flight extended axial field-of-view PET∕CT camera. METHODS: The International Electrotechnical Commission (IEC) body phantom was used to image six spheres of varying diameters containing a high concentration of (90)Y solution in a lower concentration background. Multiple PET studies were acquired of the phantom over a number of days during decay. The effect of reconstruction parameters in OSEM was evaluated both qualitatively and quantitatively. Expected values of total phantom activity, hot-sphere, and background concentration were compared to measured values from the reconstructed data as well as misplaced events in a cold insert. The partial volume effect was measured and the effects of time-of-flight during reconstruction on hot contrast recovery and background variability were evaluated according to NEMA-NU2-2007 protocol, and compared to that for (18)F. The method was applied to a patient study following radioembolization to estimate actual implanted radioactivity. RESULTS: Increasing the number of OSEM iterations visually deteriorated image data and resulted in a larger overall difference of hot concentration measures when considering both count high and count poor data. The average difference between measured and true total activity and background concentration was found to be +5% and +5%, respectively. Measured hot-sphere concentration was linear across all datasets, and while estimated to be within error of expected values, was consistently underestimated by an average of 23%, 12%, and 8%, when using a CT-derived, 50% threshold-derived, and 70% threshold-derived volume of interest, respectively. Partial volume effects were evident in all but the largest sphere, following an expected relationship between object size and recovery coefficient, inferior to that of (18)F. Time-of-flight improved contrast of hot-spheres but resulted in a deterioration of background variability, following a similar trend to that seen with (18)F. The patient data estimated a total implanted activity of 1643 MBq, compared to the intended dose of 1780 MBq, with a difference most likely due to residual and error in the initial dose calibration. CONCLUSIONS: Quantitative (90)Y PET with a state-of-the-art PET∕CT scanner with time-of-flight and standard corrections for photon interactions demonstrates consistent and acceptable measures of total activity and radionuclide concentration across a range of realistic count statistics. The method is suitable for measuring the radioactivity delivered at the time of (90)Y therapy with the potential for absorbed dose calculation.

Validation of longitudinal DXA changes in body composition from pre- to mid-adolescence using MRI as reference.

Dual-energy X-ray absorptiometry (DXA) has been used extensively for bone mineral density and body composition assessments. Surprisingly, the role of DXA in monitoring changes in children's body composition, using direct imaging methods such as magnetic resonance imaging (MRI) as reference, is still yet to be validated. We aimed at validating the use of DXA in monitoring change in the thigh lean soft tissue mass (LSTM) and fat mass (FM) when compared with thigh skeletal muscle mass (SM) and FM, measured using MRI as the reference standard, from childhood to midadolescence. At baseline, 22 healthy children (16 boys and 6 girls) aged 8-11yr were included, and then recalled at pubertal stage Tanner2-Tanner4. LSTM-DXA and FM-DXA of the mid-third femur and SM-MRI and FM-MRI of the same region were measured on the same day. The same protocol was repeated 26-48mo later. At baseline, DXA overestimated LSTM-DXA on average by 222g (95% confidence interval [CI]: 33-410g) with a concordance C-LSTM=0.576. FM-MRI and FM-DXA were not significantly different (95% CI=213 to 199g, the C-FM=0.907). At follow-up, change in LSTM-DXA and FM-DXA were not significantly different to change in SM-MRI and FM-MRI, respectively (95% CI of the difference was -278 to 208g for LSTM, and -148 to 236g for FM). The coefficient of concordance between the 2 techniques was 0.88 for both LSTM and FM. This study validates the use of DXA in monitoring changes in LSTM and FM in children, confirming its significant potential in clinical and research roles in pediatric body composition.